This invention relates to systems and methods for correcting detector decision errors. In particular, systems and methods are disclosed for correcting decision errors if the errors are of a degree that exceeds the correction capability of an error-correction code.
In the area of information storage and communication, data generally exist in the form of electromagnetic signals. These signals are stored on signal bearing media and/or are carried on a communication channel where they are susceptible to being affected by interference signals, defects in the signal bearing media, or other phenomena. In relation to a signal containing data of interest, the interference signals and other phenomena can be generally characterized as “noise”, and a signal of interest affected by noise can be referred to as a “noisy signal.”
As used herein, a detector is a device that receives a noisy signal and attempts to decide, from the noisy signal, what the original data was. Because the noisy signal may be vastly different from the original (non-noisy) signal, errors can occur in a detector's decisions. Different types of detectors make the decisions with varying degrees of success. However, under certain conditions, even the most effective detectors can make incorrect decisions.
If a detector makes an incorrect decision, the time and resources required for another copy of the data to be re-generated or re-communicated can be nontrivial. One way to mitigate the commitment of such time and resources is to employ an error-correcting code (ECC) to identify and remove some or all of the decision errors made by a detector. One of the most effective ECCs is the well-known Reed-Solomon (RS) ECC. To apply the RS ECC, data of interest (called a dataword) are encoded by an RS encoder to provide encoded data (called a codeword), which is communicated as a signal. A detector receives a noisy signal corresponding to the codeword and decides, from the noisy signal, what the codeword was. An RS decoder then decodes the decisions to provide a resulting, decoded dataword. RS decoding works in a way that corrects none or all of the errors in a detector's decisions (not counting decoder error, i.e. mis-correction). Thus, if all of the errors in the decisions were corrected, the decoded dataword would be the same as the dataword provided to the RS encoder.
Information storage and communication is an area of ongoing research, and there is continued interest in improving the RS ECC. Of particular interest is a method known as soft-output decoding, in which a detector generates decisions and also generates reliability metrics that represent how confident it is about the decisions. U.S. patent application Ser. No. 09/904,507, which is commonly owned, describes soft-output decoding for controlled intersymbol interference channels. Also of particular interest is a method known as List ECC decoding, which is described in U.S. patent application Ser. Nos. 10/135,422 and 10/313,651. While soft-output decoding and list ECC decoding are effective, their implementation can be costly. Thus, there is continued interest in improving their technology and implementation.